Mucociliary Clearance and Its Importance

Abstract

Nasal airway, which is exposed to a variety of noxious agents, transports tremendous amount of air into the lungs during normal respiration. Nasal cavity is lined mostly with the ciliated pseudostratified columnar epithelium, whereas the paranasal sinuses are lined with the ciliated simple columnar epithelium. Nasal mucosa is considered as the first-line defence against airborne particles through its mucosal surface which maintains intimate contact with the environment. There are many mechanisms that are acting together to protect the host: mucosal barrier function, mucociliary clearance (MCC), inherent phagocytes, and secretion of a variety of proteins. Airway surface is covered with a two-layered coating composed of periciliary layer (periciliary fluid) and mucus layer. Cilia of the epithelial cells move in a coordinated fashion in order to propel the pathogens and particles. MCC is driven by the coordinated action of the cilia. The coating of the airway surface is also called airway surface fluid (ASL) and airway epithelia are known to have a role in regulation of the volume and/or composition of the ASL. Paranasal sinuses depend solely on MCC mechanism to clear mucus, whereas nasal cavity takes the advantages of sneeze and cough reflexes in addition to MCC (Antunes MB, Cohen NA. Curr Opin Allergy Clin Immunol. 7:5–10; 2007). Cough and sneezing may become even more prominent in mucus transport in the presence of pathologic conditions. Coordinated ciliary activity of the epithelium along with intact mucus and periciliary layer production is needed for an effective MCC. Failure of the ciliary activity and/or the production of the mucus-periciliary layer lead to serious disorders.